Ciguatera poisoning is a particular type of fish poisoning which results from the ingestion of contaminated fish. Intoxication is associated with the consumption of toxins produced by the tropical dinoflagellates, including Gambierdiscus toxicus, which are subsequently passed along the marine food chain to man. Ciguatoxins are polyether marine toxins, and approximately 27 different ciguatoxins are known, approximately 23 of which are toxic to man. Ciguatera toxins are odorless, tasteless, heat-stable, and generally undetectable by simple chemical tests.
Humans are susceptible to ciguatera poisoning, both from eating toxic herbivores which ingest the dinoflagellates while feeding on red or brown algae, and from eating carnivores which have eaten the toxic herbivores. An accurate assessment of the incidence of ciguatera poisoning is not available; however, it is estimated that, each year, from 10,000 to 50,000 people who live in or visit tropical and subtropical areas suffer from ciguatera poisoning. Additionally, the threat of this contamination results in enormous economic losses in the recreational and commercial exploitation of fishery resources in the affected areas. With increased utilization of tropical reef fish in the continental United States, through interstate commercial trade and tourist travel, incidents of ciguatera poisoning are on the increase.
The onset of the clinical symptoms of ciguatera poisoning occurs within 10 minutes to 24 hours following the consumption of contaminated fish. Ciguatera poisoning affects the digestive system (resulting in abdominal pain, diarrhea, vomiting, nausea); the cardiovascular system (resulting in bradycardia, hypotension, tachycardia); and the neurological system (resulting primarily in paraesthesia and dysesthesia).
Immunological methods have been developed for the identification of ciguatoxin in fish, such as those described in U.S. Pat. No. 4,816,392. These methods offer a relatively simple method of assaying for ciguatoxin. However, such assays incorporate the requirement for "controls." Positive and negative controls are necessary in such assay reactions so that the user of the assay can determine if the reagents are functioning correctly. Also, positive and negative controls provide standard reactions with which the user can compare test assay results to determine if a positive or negative reaction has been obtained. The term "positive control" as used herein means a composition which reacts with antibodies or other assay reagents in a manner similar to ciguatoxin-containing fish extracts to give a positive reaction when assayed. The term "negative control" refers to a sample which contains all the components of a test assay sample, except for a ciguatoxin-containing fish extract or such toxins, and which does not react with antibodies against ciguatoxin, therefore giving a negative reaction when assayed.
Previously, fish extracts have been used as a positive control for ciguatoxin assays. However, such extracts vary in their composition, with respect to the ciguatoxins they contain and the concentration of the ciguatoxin(s) present, and, therefore, also vary in their reactivity. As a result, fish extracts exhibit variable reactivity and give results that are not reproducible. Also, to determine the toxicity of ciguatoxin in fish extracts, toxicity assays, such as assaying the toxicity of the ciguatoxin in mice, have to be performed. Such assays are time-consuming and expensive.
An additional drawback of the use of fish ciguatoxin extracts is that, for mass production of kits for the assaying of fish which may contain ciguatoxin or other "screening" assay methods, enormous numbers of toxic fish would be required for the production of ciguatoxin extract for the positive controls. The requirement for such large amounts of ciguatoxin extracts could make the routine testing of fish impractical or too expensive to be feasible, and results would vary with different fish ciguatoxin extract preparations.
There exists a need, therefore, for a composition which will reliably and reproducibly react in a ciguatoxin assay to mimic the results that would be obtained with a ciguatoxin-contaminated fish and which is readily available and relatively inexpensive.